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1.
Hydrogen peroxide, produced by inflammatory and vascular cells, induces oxidative stress that may contribute to endothelial dysfunction. In smooth muscle cells, H 2O 2 induces production of O 2− by activating NADPH oxidase. However, the mechanisms whereby H 2O 2 induces oxidative stress in endothelial cells are poorly understood. We examined the effects of H 2O 2 on O 2− levels on porcine aortic endothelial cells (PAEC). Treatment with 60 μmol/L H 2O 2 markedly increased intracellular O 2− levels (determined by conversion of dihydroethidium to hydroxyethidium) and produced cytotoxicity (determined by propidium iodide staining) in PAEC. Overexpression of human manganese superoxide dismutase in PAEC reduced O 2− levels and attenuated cytotoxicity resulting from treatment with H 2O 2. L-NAME, an inhibitor of nitric oxide synthase (NOS), and apocynin, an inhibitor of NADPH oxidase, reduced O 2− levels in PAEC treated with H 2O 2, suggesting that both NOS and NADPH oxidase contribute to H 2O 2-induced O 2− in PAEC. Inhibition of NADPH oxidase using apocynin and NOS rescue with L-sepiapterin together reduced O 2− levels in PAEC treated with H 2O 2 to control levels. This suggests interaction-distinct NOS and NADPH oxidase pathways to superoxide. We conclude that H 2O 2 produces oxidative stress in endothelial cells by increasing intracellular O 2− levels through NOS and NADPH oxidase. These findings suggest a complex interaction between H 2O 2 and oxidant-generating enzymes that may contribute to endothelial dysfunction. 相似文献
2.
Human neutrophils (PMN) activated by N-formyl-methionyl-leucyl-phenylalanine (fMLP) simultaneously release nitric oxide (.NO), superoxide anion (O 2-) and its dismutation product, hydrogen peroxide (H 2O 2). To assess whether NO production shares common steps with the activation of the NADPH oxidase, PMN were treated with inhibitors and antagonists of intracellular signaling pathways and subsequently stimulated either with fMLP or with a phorbol ester (PMA). The G-protein inhibitor, pertussis toxin (1-10 μg/ml) decreased H 2O 2 yield without significantly changing. NO production in fMLP-stimulated neutrophils; no effects were observed in PMA-activated cells. The inhibition of tyrosine kinases by genistein (1-25 μg/ml) completely abolished H 2O 2 release by fMLP-activated neutrophils; conversely, NO production increased about 1.5- and 3-fold with fMLP and PMA, respectively. Accordingly, orthovanadate, an inhibitor of phosphotyrosine phosphatase, markedly decreased -NO production and increased O 2;- release. On the other hand, inhibition of protein kinase C with staurosporine and the use of burst antagonists like adenosine, cholera toxin or dibutyryl-cAMP diminished both H 2O 2 and NO production. The results suggest that the activation of the tyrosine kinase pathway in stimulated human neutrophils controls positively O 2- and H 2O 2 generation and simultaneously maintains -NO production in low levels. In contrast, activation of protein kinase C is a positive modulator for O 2;-and *NO production. 相似文献
3.
Incubation of rat-liver microsomes, previously azide-treated to inhibit catalase, with H 2O 2 caused a loss of cytochrome P-450 but not of cytochrome b 5. This loss of P-450 was not prevented by scavengers of hydroxyl radical, chain-breaking antioxidants or metal ion-chelating agents. Application of the thiobarbituric acid (TBA) assay to the reaction mixture suggested that H 2O 2 induces lipid peroxidation, but this was found to be due largely or completely to an effect of H 2O 2 on the TBA assay. By contrast, addition of ascorbic acid and Fe(III) to the microsomes led to lipid peroxidation and P-450 degradation: both processes were inhibited by chelating agents and chain-breaking antioxidants, but not by hydroxyl radical scavengers. H 2O 2 inhibited ascorbate/Fe (III)-induced microsomal lipid peroxidation, but part of this effect was due to an action of H 2O 2 in the TBA test itself. H 2O 2 also decreased the colour measured after carrying out the TBA test upon authentic malondialdehyde, tetraethoxypropane, a DNA-Cu 2+/ o-phenanthroline system in the presence of a reducing agent, ox-brain phospholipid liposomes in the presence of Fe(III) and ascorbate, or a bleomycin-iron ion/DNA/ascorbate system. Caution must be used in interpreting the results of TBA tests upon systems containing H 2O 2. 相似文献
4.
各种环境介质和生命体中许多微观化学过程都与活性氧密切相关.本文介绍了水环境中活性氧的来源、种类和测定.它们主要包括: 1O 2(单线态氧)、O 2-(超氧自由基)/HO 2·(氢过氧自由基)、·OH(羟基自由基)、H 2O 2、RO·(烷氧基)、ROO·(烷过氧基)和R·OH(氢过氧化物)等.其主要来源于辐射分解、热解和氧化还原法等.测定采用分子探针法、图谱法和酶法. 相似文献
5.
In the gingival crevicular fluid (GCF) of control and chronic adult periodontitis (CAP) patients there is a spontaneous release of O 2- radicals from polymorphonuclear leukocytes (PMN). The addition of the exogenous stimuli phorbol myrystate acetate (PMA) decreased the O 2- formation in control GCF, while in CAP patients produced a marked enhancement of O 2- generation.
The circulating PMN of control subjects did not show a spontaneous O 2- formation, differently from CAP patients. On the contrary, a similar O 2- production was measured when the circulating PMN were stimulated with PMA.
Moreover, the antioxidant activity measured in 10μl of cell free gingival supernatant (GS) of control and CAP patients had the same values by inhibiting 12.6% and 18.9% respectively of the O 2- formation supported by a xanthine/xanthine oxidase system.
Probably, the protective or destructive effect of PMN in GCF of CAP patients depends on the variations of the rate of O 2- formation in respect to the intrinsic antioxidant property of GS. 相似文献
6.
Alcohol dehydrogenase (ADH) was used as a marker molecule to clarify the mechanism of gastric mucosal damage as a side effect of using piroxicam. Piroxicam inactivated ADH during interaction of ADH with horseradish peroxidase and H 2O 2 (HRP-H 2O 2). The ADH was more easily inactivated under aerobic than anaerobic conditions, indicating participation by oxygen. Superoxide dismutase, but not hydroxyl radical scavengers, inhibited inactivation of ADH, indicating participation by superoxide. Sulfhydryl (SH) groups in ADH were lost during incubation of piroxicam with HRP-H 2O 2. Adding reduced glutathione (GSH) efficiently blocked ADH inactivation. Other SH enzymes, including creatine kinase and glyceraldehyde-3-phosphate dehydrogenase, were also inactivated by piroxicam with HRP-H 2O 2. Thus SH groups in the enzymes seem vulnerable to piroxicam activated by HRP-H 2O 2. Spectral change in piroxicam was caused by HRP-H 2O 2. ESR signals of glutathionyl radicals occurred during incubation of piroxicam with HRP-H 2O 2 in the presence of GSH. Under anaerobic conditions, glutathionyl radical formation increased. Thus piroxicam free radicals interact with GSH to produce glutathionyl radicals. Piroxicam peroxyl radicals or superoxide, or both, seem to inactivate ADH. Superoxide may be produced through interaction of peroxyl radicals with H 2O 2. Thus superoxide dismutase may inhibit inactivation of ADH through reducing piroxicam peroxyl radicals or blocking interaction of SH groups with O 2-, or both. Other oxicam derivatives, including isoxicam, tenoxicam and meloxicam, induced ADH inactivation in the presence of HRP-H 2O 2. 相似文献
7.
The production of singlet oxygen by H 2O 2 disproportionation and via the oxidation of H 2O 2 by NaOCl in a neutral medium was monitored by spin trapping with 2,2,6,6 tetramethyl-4-piperidone (TMPone). The singlet oxygen formed in both reactions oxidized 2,2,6,6 tetramethyl-4-piperidone to give nitroxide radicals. However the production of nitroxide radicals was relatively small considering the concentrations of H 2O 2 and NaOCl used in the reaction systems. Addition of electron donating agents: ascorbate, Fe 2+ and desferrioxamine leads to an increase in the production of nitroxide radicals. We assumed that a very slow step of the reaction sequence, the homolytic breaking of the O-O bond of N-hydroperoxide (formed as an intermediate product during the reaction of 1O 2 with TMPone) could be responsible for the relatively small production of nitroxide radicals. Electron donating agents added to the reaction system probably raise the rate of the hydroperoxide decomposition by allowing a more rapid heterolytic cleavage of the O-O bond leading to a greater production of nitroxide radicals. The largest effect was observed in the presence of desferrioxamine. Its participation in this process is proved by the concomitant appearance of desferrioxamine nitroxide radicals. The results obtained demonstrate that the method proposed by several authors and tested in this study to detect singlet oxygen is not convenient for precise quantitative studies. The reactivity of TMPone towards O 2-7HO 2' and 'OH has been also investigated. It has been found that both O 2-7HO 2' and 'OH radicals formed in a phosphate buffer solution (pH 7.4, 37°C), respectively by a xanthine-oxidase/hypoxanthine system and via H 2O 2 UV irradiation, do not oxidize 2,2,6,6 tetramethyl-4-piperidone to nitroxide radicals. 相似文献
8.
Thioctic acid (TA) and its reduced form dihydrolipoic acid (DHLA) have recently gained somc recognition as useful biological antioxidants. In particular, the ability of DHLA to inhibit lipid peroxidation has been reported. In the present study, the effects of TA and DHLA on reactive oxygen species (ROS) generated in the aqueous phase have been investigated. Xanthine plus xanthine oxidase-generated superoxide radicals (O 2), detected by electron spin resonance spectroscopy (ESR) using DMPO as a spin trap. were eliminated by DHLA but not by TA. The sulhydryl content of DHLA, measured using Ellman's reagent decreased subsequent to the incubation with xanthine plus xanthine oxidase confirming the interaction between DHLA and O 2-. An increase of hydrogen peroxide concentration accompanied the reaction between DHLA and O 2x, suggesting the reduction of O 2- by DHLA. Competition of O 2- with epinephrine allowed us to estimate a second order kinetic constant of the reaction between O 2- and DHLA, which was found to be a 3.3 × 10 5 M -1 s -1. On the other hand, the DMPO signal of hydroxyl radicals (HO ·) generated by Fenton's reagent were eliminated by both TA and DHLA. Inhibition of the Fenton reaction by TA was confirmed by a chemiluminescence measurement using luminol as a probe for HO ·. There was no electron transfer from Fe 2+ to TA or from DHLA to Fe 3 + detected by measuring the Fe 2+ -phenanthroline complex. DHLA did not potentiate the DMPO signal of HO · indicating no prooxidant activity of DHLA. These results suggest that both TA and DHLA possess antioxidant properties. In particular. DHLA is very effective as shown by its dual capability by eliminating both O 2-; and HO ·. 相似文献
9.
Trehalose is known to protect membranes and macromolecules. Its accumulation has been implicated in allowing plants to tolerate stress, including heat-shock. However, under heat-shock, it is not clear whether trehalose eliminates reactive oxygen species (ROS) directly or indirectly by protecting antioxidant enzymes. In this study, we initially examined the effects of trehalose on the activities of key antioxidant enzymes, including superoxide dismutases (SODs), ascorbate catalases (CATs), and ascorbate peroxidases (APX) from wheat ( Triticum aestivum L.), and then measured the ability of trehalose to scavenge hydrogen peroxide (H 2O 2) and superoxide anions (O 2−). Our results indicated that trehalose protected SOD activity slightly. However, it inhibited CAT and APX activities under heat stress, with a little protection of CAT activity (only about 7% promotion) at 22 °C. Moreover, trehalose scavenged H 2O 2 and O 2− greatly in a concentration-dependent manner, reaching the maximal scavenging H 2O 2 rate of 95% and O 2− rate of 78%, respectively, at 50 mM trehalose. These results suggest that trehalose plays a direct role in eliminating H 2O 2 and O 2− in wheat under heat stress. 相似文献
10.
Heme catalases are considered to degrade two molecules of H 2O 2 to two molecules of H 2O and one molecule of O 2 employing the catalatic cycle. We here studied the catalytic behaviour of bovine liver catalase at low fluxes of H 2O 2 (relative to catalase concentration), adjusted by H 2O 2-generating systems. At a ratio of a H 2O 2 flux (given in μM/min - 1) to catalase concentration (given in μM) of 10 min - 1 and above, H 2O 2 degradation occurred via the catalatic cycle. At lower ratios, however, H 2O 2 degradation proceeded with increasingly diminished production of O 2. At a ratio of 1 min - 1, O 2 formation could no longer be observed, although the enzyme still degraded H 2O 2. These results strongly suggest that at low physiological H 2O 2 fluxes H 2O 2 is preferentially metabolised reductively to H 2O, without release of O 2. The pathways involved in the reductive metabolism of H 2O 2 are presumably those previously reported as inactivation and reactivation pathways. They start from compound I and are operative at low and high H 2O 2 fluxes but kinetically outcompete the reaction of compound I with H 2O 2 at low H 2O 2 production rates. In the absence of NADPH, the reducing equivalents for the reductive metabolism of H 2O 2 are most likely provided by the protein moiety of the enzyme. In the presence of NADPH, they are at least in part provided by the coenzyme. 相似文献
11.
The effects of nitric oxide (NO) on xanthine oxidase (XOD) activity and the site(s) of the redox center(s) affected were investigated. XOD activity was determined by superoxide (O 2-) generation and uric acid formation. NO reversibly and dose-dependently suppressed XOD activity in both determination methods. The suppression interval also disclosed a dose-dependent prolongation. The suppression occurred irrespective of the presence or absence of xanthine; indicating that the reaction product of NO and O 2-, peroxynitrite, is not responsible for the suppression. Application of synthesized peroxynitrite did not affect XOD activity up to 2 μM. Methylene blue, which is an electron acceptor from Fe/S center, prevented the NO-induced inactivation. The results indicate that NO suppresses XOD activity through reversible alteration of the flavin prosthetic site. 相似文献
12.
Recent studies have demonstrated that nitric oxide (NO) in the presence of superoxide (O 2-) may mediate mutagenesis via the N-nitrosation of DNA bases followed by nitrosative deamination to yield their hydroxylated derivatives. We have found that phorbol myristate acetate (PMA)-activated extravasated rat neutrophils (PMNs) will N-nitrosate 2,3-diaminonaphthalene (DAN) to yield its highly fluorescent nitrosation product 2,3- naphthotriazole (triazole) via the L-arginine dependent formation of NO. Addition of SOD enhanced triazole formation suggesting that O 2- production may inhibit the N-nitrosating activity and thus the mutagenic activity of inflammatory PMNs. The objective of this study was to assess the role of superoxide as a modulator of NO-dependent N-nitrosation reactions using PM A-activated PMNs as well as a chemically defined-system that generates both NO and superoxide. We found that PMA-activation of PMNs reduced the amount of N-nitrosation of DAN by approximately 64% when compared to non- stimulated cells (450 vs. 1250 nM). Addition of SOD but not inactivated SOD or catalase to PMA-activated PMNs enhanced the formation of triazole by approximately 4-fold (1950 nM). In addition, we found that the NO-releasing spermine/NO adduct (Sp/NO; 50μM) which produces approximately 1.0 nmol NO/min generated approximately 8000 nM of triazole whereas the combination of Sp/NO and a superoxide generator (hypoxanthine/xanthine oxidase) that produces approximately 1.0 nmol O 2-/min reduced triazole formation by 90% (790 nM). Addition of SOD but not catalase restored the N-nitrosating activity. We conclude that equimolar fluxes of superoxide react rapidly with NO to generate products that have only limited ability to N-nitrosate aromatic amino compounds and thus may have limited ability to promote mutagenesis via the nitrosative deamination of DNA bases. 相似文献
13.
以白菜型油菜‘陇油6号’和‘天油2号’为试验材料,经MAPK抑制剂U0126、H_2O_2清除剂DMTU、NADPH氧化酶抑制剂DPI和IMD预处理后再分别进行盐胁迫、PEG-6000模拟干旱胁迫,研究其对两种油菜幼苗活性氧、抗氧化酶活性和RbohC、RbohF基因表达的影响.结果表明:盐胁迫和PEG-6000模拟干旱胁迫下,两种白菜型油菜中H_2O_2积累量上升,O_2 -·积累量下降,抗氧化酶(超氧化物歧化酶SOD、过氧化氢酶CAT、抗坏血酸过氧化物酶APX和谷胱甘肽还原酶GR)活性和RbohC、RbohF基因表达均升高.与单独胁迫处理相比,两种油菜O_2 -·积累、抗氧化酶活性和RbohC、RbohF基因的表达量均明显降低,经DMTU、DPI和IMD预处理后再分别进行盐和干旱胁迫,H_2O_2积累量下降,但U0126预处理后再进行胁迫处理,H_2O_2积累量上升.说明NADPH氧化酶、MAP激酶级联途径、H_2O_2参与了盐、干旱胁迫下活性氧产生、抗氧化酶活性变化和RbohC、RbohF基因表达的调控. 相似文献
14.
The effects of xanthine + xanthine oxidase-generated reactive oxygen species (ROS) on rabbit muscle creatine kinase (CK) were studied. Xanthine (0.1 mM) + xanthine oxidase (30 mU/ml) inhibited activity of rabbit muscle CK (1.2mU/ml). Catalase (100/ml), but not SOD (100 U/ml), deferoxamine (100μM) or mannitol (20 mM), protected CK from inactivation; suggesting that H 2O 2 was responsible for inactivation. These results were different from previously reported findings on bovine heart CK that superoxide radicals inactivate the enzyme. Thus, enzymes with homologous structures may have different reactivities to different ROS. H 2O 2-induced inactivation of rabbit muscle CK was accompanied by a decrease in its thiol group content, whereas no significant changes in the protein structure were detected by SDS-PAGE or carbonyl content. These results suggest that oxidation of -SH groups by H 2O 2 seems to be a major mechanism of activation of rabbit muscle CK by xanthine + xanthine oxidase. Such inactivation of CK by H 2O 2 may be important in ROS-induced pathology. 相似文献
15.
The role of histidine on DNA breakage induced by hydrogen peroxide (H 2O 2) and ferric ions or by H 2O 2 and cupric ions was studied on purified DNA. L-histidine slightly reduced DNA breakage by H 2O 2 and Fe 3+ but greatly inhibited DNA breakage by H 2O 2 and Cu 2+. However, only when histidine was present, the addition of EDTA to H 2O 2 and Fe 3+ exhibited a bimodal dose response curve depending on the chelator metal ratio. The enhancing effect of histidine on the rate of DNA degradation by H 2O 2 was maximal at a chelator metal ratio between 0.2 and 0.5, and was specific for iron. When D-histidine replaced L-histidine, the same pattern of EDTA dose response curve was observed. Superoxide dismutase greatly inhibited the rate of DNA degradation induced by H 2O 2, Fe 3+, EDTA and L-histidine involving the superoxide radical.
These studies suggest that the enhancing effect of histidine on the rate of DNA degradation by H 2O 2 and Fe 3+ is mediated by an oxidant which could be a ferrous-dioxygen-ferric chelate complex or a chelate-ferryl ion. 相似文献
16.
1. 1. The mechanism of the photooxidation of ascorbate and of Mn2+ by isolated chloroplasts was reinvestigated. 2. 2. Our results suggest that ascorbate or Mn2+ oxidation is the result of the Photosystem I-mediated production of the radical superoxide, and that neither ascorbate nor Mn2+ compete with water as electron donors to Photosystem II nor affect the rate of electron transport through the two photosystems: The radical superoxide is formed as a result of the autooxidation of the reduced forms of low potential electron acceptors, such as methylviologen, diquat, napthaquinone, or ferredoxin. 3. 3. In the absence of ascorbate or Mn2+ the superoxide formed dismutases either spontaneously or enzymatically producing O2 and H2O2. In the presence of ascorbate or Mn2+, however, the superoxide is reduced to H2O2 with no formation of O2. Consequently, in the absence of reducing compounds, in the reaction H2O to low potential acceptor one O2 (net) is taken up per four electrons transported where as in the presence of ascorbate, Mn2+ or other suitable reductants up to three molecules O2 can be taken up per four electrons transported. 4. 4. This interpretation is supported by the following observations: (a) in a chloroplast-free model system containing NADPH and ferredoxin-NADP reductase, methylviologen can be reduced to a free radical which is autooxidizable in the presence of O2; the addition of ascorbate or Mn2+ to this system results in a two fold stimulation of O2 uptake, with no stimulation of NADPH oxidation. The stimulation of O2 uptake is inhibited by the enzyme superoxide dismutase; (b) the stimulation of light-dependent O2 uptake in the system H2O → methylviologen in chloroplasts is likewise inhibited by the enzyme superoxide dismutase. 5. 5. In Class II chloroplasts in the system H2O → NADP upon the addition of ascorbate or Mn2+ an apparent inhibition of O2 evolution is observed. This is explained by the interaction of these reductants with the superoxide formed by the autooxidation of ferredoxin, a reaction which proceeds simultaneously with the photoreduction of NADP. Such an effect usually does not occur in Class I chloroplasts in which the enzyme superoxide dismutase is presumably more active than in Class II chloroplasts. 6. 6. It is proposed that since in the Photosystem I-mediated reaction from reduced 2,4-dichlorophenolindophenol to such low potential electron acceptor as methylviologen, superoxide is formed and results in the oxidation of the ascorbate present in the system, the ratio ATP/2e in this system (when the rate of electron flow is based on the rate of O2 uptake) should be revised in the upward direction.
Abbreviations: DCMU, 3-(3′,4′-dichlorophenyl)-1,1-dimethylurea; HEPES, hydroxyethyl-piperazineethanesulfonic acid; MES, (N-morpholino)ethanesulfonic acid; DCIP, 2,4-dichlorophenol-indophenol 相似文献
17.
以白菜型油菜‘陇油6号’和‘天油2号’为试验材料,经MAPK抑制剂U0126、H 2O 2清除剂DMTU、NADPH氧化酶抑制剂DPI和IMD预处理后再分别进行盐胁迫、PEG-6000模拟干旱胁迫,研究其对两种油菜幼苗活性氧、抗氧化酶活性和 RbohC、 RbohF基因表达的影响.结果表明: 盐胁迫和PEG-6000模拟干旱胁迫下,两种白菜型油菜中H 2O 2积累量上升,O 2-·积累量下降,抗氧化酶(超氧化物歧化酶SOD、过氧化氢酶CAT、抗坏血酸过氧化物酶APX和谷胱甘肽还原酶GR)活性和 RbohC、 RbohF基因表达均升高.与单独胁迫处理相比,两种油菜O 2-·积累、抗氧化酶活性和 RbohC、 RbohF基因的表达量均明显降低,经DMTU、DPI和IMD预处理后再分别进行盐和干旱胁迫,H 2O 2积累量下降,但U0126预处理后再进行胁迫处理,H 2O 2积累量上升.说明NADPH氧化酶、MAP激酶级联途径、H 2O 2参与了盐、干旱胁迫下活性氧产生、抗氧化酶活性变化和 RbohC、 RbohF基因表达的调控. 相似文献
18.
The toxicity of H 2O 2 in Escherichia coli wild type and superoxide dismutase mutants was investigated under different experimental conditions. Cells were either grown aerobically, and then treated in M9 salts or K medium, or grown anoxically, and then treated in K medium. Results have demonstrated that the wild type and superoxide dismutase mutants display a markedly different sensitivity to both modes of lethality produced by H 2O 2 (i.e. mode one killing, which is produced by concentrations of H 2O 2 lower than 5 mM, and mode two killing which results from the insult generated by concentrations of H 2O 2 higher than 10 mM). Although the data obtained do not clarify the molecular basis of H 2O 2 toxicity and/or do not explain the specific function of superoxide ions in H 2O 2-induced bacterial inactivation, they certainly demonstrate that the latter species plays a key role in both modes of H 2O 2 lethality. A mechanism of H 2O 2 toxicity in E. coli is proposed, involving the action of a hypothetical enzyme which should work as an O 2-• generating system. This enzyme should be active at low concentrations of H 2O 2 (<5 mM) and high concentrations of the oxidant (>5 mM) should inactivate the same enzyme. Superoxide ions would then be produced and result in mode one lethality. The resistance at intermediate H 2O 2 concentrations may be dependent on the inactivation of such enzyme with no superoxide ions being produced at levels of H 2O 2 in the range 5–10 mM. Mode two killing could be produced by the hydroxyl radical in concert with superoxide ions, chemically produced via the reaction of high concentrations of H 2O 2 (>10 mM) with hydroxyl radicals. The rate of hydroxyl radical production may be increased by the higher availability of Fe 2+ since superoxide ions may also reduce trivalent iron to the divalent form. 相似文献
19.
Electron spin resonance spin trapping was utilized to investigate free radical generation from cobalt (Co) mediated reactions using 5,5-dimethyl-l-pyrroline (DMPO) as a spin trap. A mixture of Co with water in the presence of DMPO generated 5,5-dimethylpyrroline-(2)-oxy(1) DMPOX, indicating the production of strong oxidants. Addition of superoxide dismutase (SOD) to the mixture produced hydroxyl radical ( OH). Catalase eliminated the generation of this radical and metal chelators, such as desferoxamine, diethylenetriaminepentaacetic acid or 1,10-phenanthroline, decreased it. Addition of Fe(II) resulted in a several fold increase in the OH generation. UV and O 2 consumption measurements showed that the reaction of Co with water consumed molecular oxygen and generated Co(II). Since reaction of Co(II) with H 2O 2 did not generate any significant amount of OH radicals, a Co(I) mediated Fenton-like reaction [Co(I) + H 2O 2 → Co(II) + OH + OH −] seems responsible for OH generation. H 2O 2 is produced from O 2− via dismutation. O 2− is produced by one-electron reduction of molecular oxygen catalyzed by Co. Chelation of Co(II) by biological chelators, such as glutathione or β-ananyl-3-methyl-
-histidine alters, its oxidation–reduction potential and makes Co(II) capable of generating OH via a Co(II)-mediated Fenton-like reaction [Co(II) + H 2O 2 → Co(III) + OH + OH −]. Thus, the reaction of Co with water, especially in the presence of biological chelators, glutathione, glycylglycylhistidine and β-ananyl-3-methyl-
-histidine, is capable of generating a whole spectrum of reactive oxygen species, which may be responsible for Co-induced cell injury. 相似文献
20.
The embryo of oviparous species is confronted by a highly oxidative stress generating as it grows and must rely on effective antioxidant system for protection. Proteins of avian egg albumin have been suggested to play the major redox-modulatory role during embryo development. Recently, we found that ovotransferrin (OTf) undergoes distinct thiol-linked self-cleavage in a redox-dependent process. In this study, we explore that OTf is SOD mimic protein with a potent superoxide anion (O 2−) scavenging activity. The O 2− scavenging activity was investigated using the natural xanthine/xanthine oxidase (X/XOD) coupling system. OTf exhibited O 2− scavenging activity in a dose-dependent manner and showed remarkably higher scavenging activity than the known antioxidants, ascorbate or serum albumin. The isolated half-molecules of OTf exhibited higher scavenging activity than the intact molecule, whereas the N-lobe showed much greater activity. OTf dramatically quenched the O 2− flux but had no effect on the urate production in the X/XOD system, indicating its unique specificity to scavenge O 2− but not oxidase inhibition. Strikingly, metal-bound OTf exhibited greater O 2− dismutation capacity than the apo-protein, ranging from moderate (Zn 2+-OTf and Fe 2+-OTf) to high (Mn 2+-OTf and Cu 2+-OTf) activity with the Cu 2+-OTf being the most potent scavenger. In a highly sensitive fluorogenic assay, the metal-bound OTf exhibited significant increase in the rate of H 2O 2 production in the X/XOD reaction than the apo-OTf, providing evidence that Zn 2+-, Mn 2+- and Cu 2+-OTf possess SOD mimic activity. This finding is the first to describe that OTf is an O 2− scavenging molecule, providing insight into its novel SOD-like biological function, and heralding a fascinating opportunity for its potential candidacy as antioxidant drug. 相似文献
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